(57) A 5-substituted amino-4-hydroxy-pentenoic acid or its salt represented by the formula:
wherein each of R¹ and R² which may be the same or different is a hydrogen atom,
a lower alkyl group, an aralkyl group, a lower alkoxycarbonyl group, an aryloxycarbonyl
group, an aralkyloxycarbonyl group or a lower alkanoyl group which may be substituted
by from one to three substituents selected from the group consisting of an amino group,
a hydroxyl group, a carboxyl group, an aryloxy group, an aralkyloxycarbonylamino group,
a lower alkoxycarbonylamino group and a
group (wherein each of X¹ and X² which may be the same or different is a hydrogen
atom, a lower alkyl group, an aryl group or an aralkyl group, or X¹ and X² form together
with the adjacent nitrogen atom a 5- or 6-membered heterocyclic group which may further
contain a hetero atom selected from the group consisting of a nitrogen atom, an oxygen
atom and a sulfur atom) and which may further contain a double bond in its carbon
chain, each of R³, R⁴ and R⁶ which may be the same or different is a hydrogen atom,
a lower alkyl group, a cycloalkyl group, a cycloalkylalkyl group, an aryl group, an
aralkyl group or a residue of an acidic, neutral or basic amino acid, R⁵ is a hydrogen
atom or a lower alkyl group, R⁷ is a hydrogen atom, a lower alkyl, cycloalkyl, cycloalkylalkyl
or aralkyl group which may be substituted by one or two hydroxyl groups or a residue
of an acidic, neutral or basic amino acid, R⁸ is a hydroxyl group, a -OY group (wherein
Y is a lower alkyl group, an aryl group, an aralkyl group, a lower alkoxyalkyl group,
a lower alkanoyloxyalkyl group, a lower alkoxycarbonyloxyalkyl group, or a 1-phthalidyl
group) or a
group (wherein each of Y¹ and Y² which may be the same or different is a hydrogen
atom, a lower alkyl group, an aryl group, an aralkyl group or a cycloalkyl group,
or Y¹ and Y² form together with the adjacent nitrogen atom a 5- or 6-membered heterocyclic
group which may further contain a hetero atom selected from the group consisting of
a nitrogen atom, an oxygen atom and a sulfur atom), and each of n and m which may
be the same or different is 0 or 1.
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